Part and parcel of canine communications are growls, snarls, snaps and even bites - even among the nicest of dogs and the mildest of breeds. We find these behaviors frightening, and sometimes don't quite know what to do. Unfortunately, there is a widespread misunderstanding of what constitutes aggressive behavior. Very often, what is labeled as 'aggression' is actually a useful and meaningful communication meant to avoid any violence. And at times, we overlook the fact that should a dog feel the need to act in a threatening way (whether to people, other dogs or other animals), there's a reason.
In my experience, dog behavior - especially that which we find frightening - is often poorly understood, leading to misunderstanding and frustration on both ends of the leash. No matter how fearsome we may find their behavior, we can find some relief in the knowledge that dogs act aggressively for the same basic reasons we do:
NOTE: Like humans, dogs can act aggressively in abnormal ways due to biochemical imbalances, various diseases, genetic defects, psychological and/or physical abuse, drugs or chemicals, and for reasons science cannot explain. Like their human counterparts, such abnormal dogs are rare but can be extremely dangerous.
Important Concepts in Understanding Aggression
"Aggression Basics " by Suzanne Clothier